The present application and co-pending, commonly assigned U.S. application Ser. No. 07/767,301 (C-815), and 07/768,143 (C-821), filed on even date herewith, and U.S. application Ser. No. 575,021; filed Aug. 30, 1990, now U.S. Pat. No. 5,082,072 relate to a project of the assignee of the subject invention, and share common elements of disclosure.
The subject invention relates to scales and a method of operating such scales to rapidly determine weights. More particularly, the subject invention relates to postal scales and the like.
Postal scales are well known. Such scales weigh a mail piece, and determine the appropriate postage for that mail piece as a function of the weight.
Mailing systems where a mail piece is transported onto a postal scale, the appropriate postage is determined and used to set a postage meter, and the mail piece is then transported to the postage meter for imprinting with a postal indicia representative of the postage amount are also known. One such system is described in U.S. Pat. No. 4,742,878; issued: May 10, 1988; to the inventors of the subject invention. In such systems there is a constant need to increase the rate at which the scale can determine the weight of a mail piece in order that the throughput of the system can be increased.
U.S. Pat. No. 4,787,048; issued: Nov. 22, 1988; to the inventors of the subject invention, discloses one approach to decreasing the time required for a postal scale to determine the weight of a mail piece. The system disclosed in this patent takes advantage of the structure of postal rate charts, i.e., the function which relates the weight of a mail piece to the appropriate postage amount. As can be seen in FIG. 1, such rate charts provide a constant postage value for all weights between pairs of predetermined breakpoints. The system of the '048 patent takes advantage of this by use of an algorithm where a first estimate of the weight is made and used to determine the postage amount, unless the first estimate is within a predetermined distance of a breakpoint, in which case a second more accurate estimate is made.
Another approach to providing high throughput mailing systems has been the use of vibrating tray scales to determine the weight of a mail piece where the weight is estimated as a function of the frequency at which a scale tray vibrates after a mail piece is placed upon it and the system is excited. Such a system is described in the above mentioned, commonly assigned U.S. Pat. No. 5,082,072. While such prior art systems have proven generally satisfactory there is still a need for a scale system and method of operation which are suitable for use with load cell technology while still providing desired high throughout rates for mailing systems and the like.